1. In SDES, Encryption algorithm can be written as a composition of functions:
IP-1 o fK2 o fK1 o SW o IP
a) True
b) False
Explanation: The SDES algorithm follows the order – IP-1 o fK2 o SW o fK1 o IP.
2. Assume input 10-bit key, K: 0010010111 for the SDES algorithm. What is K1?
a) 00101111
b) 01011011
c) 01101000
d) 10100111
Explanation: The permuted key P10 = 1000010111. Input to P8: 0000101111 and K1 is 00101111.
3. The Plaintext for the Ciphertext 00001111, given that the key is 1111111111 is
a) 01100111
b) 00001010
c) 11111111
d) 01101101
Explanation: Perform the SDES Decryption algorithm and compute the cipher text.
4. The Plaintext for the Ciphertext 11110000, given that the key is 0000000000 is
a) 01100111
b) 00000000
c) 01001000
d) 01101100
Explanation: Perform the SDES Decryption algorithm and compute the cipher text.
5. Assume input 10-bit key, K: 0010010111 for the SDES algorithm. What is K2?
a) 11101010
b) 11011011
c) 01101000
d) 10101111
Explanation: The permuted key P10 = 0000101111. Input to P8: 0010011101 and K2 is 11101010.
6. The Plaintext for the Ciphertext 10100101, given that the key is 0010010111 is
a) 01100111
b) 00110110
c) 01001000
d) 01001100
Explanation: Perform the SDES Decryption algorithm and compute the cipher text.
7. If a|b and b|c, then a|c.
a) True
b) False
Explanation: The statement is true. For ex, 11|66 and 66|198 = 11|198.
8. GCD(a,b) is the same as GCD(|a|,|b|).
a) True
b) False
Explanation: This is true. gcd(60,24) = gcd(60,-24) = 12.
9. Calculate the GCD of 1160718174 and 316258250 using Euclidean algorithm.
a) 882
b) 770
c) 1078
d) 1225
Explanation: GCD(1160718174, 316258250) = 1078.
10. Calculate the GCD of 102947526 and 239821932 using Euclidean algorithm.
a) 11
b) 12
c) 8
d) 6
Explanation: GCD(102947526, 239821932) = 6.